1. Field of the Invention
The present invention relates generally to a downhole oil and gas well completion tool which is operatively connectible to a lower section of tubing or a packer and configured to perform multiple completion-related functions.
2. Background Art
The harvesting of hydrocarbons from a subterranean formation involves the deployment of a drilling tool into the earth. The drilling tool is driven into the earth from a drilling rig to create a wellbore through which hydrocarbons are passed. Once a predetermined well depth is reached, the formation is tested to evaluate and determine whether the well will be completed for production, or plugged and abandoned.
Completion of a well generally refers to the operations that prepare a well bore for producing oil or gas from the reservoir. The goal of these operations is to optimize the flow of the reservoir fluids into the well bore, up through the producing string, and into the surface collection system.
The well bore is typically lined (cased) with steel pipe, and the annulus between well bore and casing is filled with cement. Properly designed and cemented casing prevents collapse of the well bore and protects fresh-water aquifers above the oil and gas reservoirs from becoming contaminated with oil and gas and the oil reservoir brine. Similarly, the oil and gas reservoir is prevented from becoming invaded by extraneous water from aquifers that were penetrated above or below the productive reservoir.
The nature of the reservoir, evaluated from a core analysis, cuttings, or logs, or from experience with similar productive formations, determines the type of completion to be used. In a barefoot completion, the casing is set just above the producing formation, and the latter is drilled out and produced with no pipe set across it. Such a completion can be used for hard rock formations which are not friable and will not slough, and when there are no opportunities for producing from another, lower reservoir. Set-through and perforated completions are also employed for relatively well-consolidated formations from which the potential for sand production is small. However, the perforated completion is used when a long producing interval must be prevented from collapse, when multiple intervals are to be completed in the one borehole, or when intervening water sands within the oil-producing interval are to be shut off and the oil-saturated intervals selectively perforated.
A string of steel tubing is lowered into the casing string and serves as the conduit for the produced fluids. The tubing may be hung from the well-head or supported by a packer set above the producing zone. The packer is used when it is desirable to isolate the casing string from the produced fluids because of the latter's pressure, temperature, or corrosivity, or when such isolation may improve production characteristics. The string, which may be referred to herein as a tubing string, may comprise any number of components known in the art. Such components, in addition to tubulars, may include tools, joints, packers, etc.
To complete the well, casing is installed and cemented in the wellbore, then production tubing is installed in the casing, which is perforated so that hydrocarbons may pass from the formation into the wellbore, and up to the tubing string to the surface for collection. Often a series of tests are conducted as a part of this process, to confirm the integrity of the casing and tubing.
When carrying out testing or other operations in a wellbore, test equipment or other apparatus may be mounted on an end portion of a string of tubular sections, known as tubulars to form a tubing string. The equipment is lowered into the bore on the end of the string, the length of the string being increased by the addition of further tubulars, which are threaded together to define a continuous internal bore between the apparatus and the surface.
A number of traditional methods exist for testing completion of a well and tubing. The most commonly used method involves the use of a wire-line retrievable plug. This process typically involves the hiring of a wire-line contractor to both run and pull the plug. The overall process is time-consuming, typically taking about 3-4 hours to set up the wire-line unit, and lower and set the plug by the wire-line. After setting the hydraulic packer and testing the completion and tubing, the wire-line operator will run the wire-line into the tubing again to retrieve the plug which might consume another 3-4 hours if no delays are encountered. Debris and impurities in the completion fluid and/or pressure trapped around the plug often result in sticking of the plug in the well. Retrieving a stuck plug can greatly increase the length of the process and may also lead to a loss of wire-line in the well, which will require the hiring of additional specialists to perform a fishing operation.
The use of the above-mentioned wire-line operation is typically feasible only if the well deviation is no greater than 70 degrees. If the testing location where the plug will need to be set is at a greater deviation, the wire-line method may not be practical and the operator must use another method of running the plug such as coiled tubing. A coiled tubing operation, once on location, takes about 5 hours to set up. Once all of the equipment is set up, running the plug by means of the coiled tubing can easily take at least 4 hours, depending on depth. The coiled tubing operation may easily cost tens of thousands of dollars in addition to the total time used to run and retrieve the plug which may exceed 10 hours, if no problems are encountered.
A more recently developed method for setting a hydraulic packer and testing the completion and tubing involves the use of a glass disc which is run inside a special pipe attached to the bottom of the tubing string. When using the glass disc method, the tubing cannot be self filled, which will require that the completions operator either manually fill the tubing via a water hose from the surface, requiring significant time, or the operator will need to add another piece of equipment to the tubing string known as a self-filling tool.
After setting the packer and testing the tubing the completions operator needs to break the glass disc in order to have the tubing opened and ready for production. If the well is not highly deviated, the wire line contractor can set up his equipment and run into the well with his tool string and break the glass disc. This operation will take around 4-5 hours.
If the well is highly deviated (more than 70 degrees) then the completions operator may need to use a coil tubing contractor to break the glass disc. Also this operation will take around 5 to 6 hours in addition to the coil tubing set up/rental cost.
Another method of setting the packer and testing the tubing is to use a pump out plug which is a special short pipe with a ball seat fixed in a seat with a number of shear screws. After running the tubing completely, a ball is dropped from the surface. It takes around 40-60 minutes until the ball seats on the ball seat, then surface pressure is applied against the ball to set the packer and test the tubing. After testing the tubing the surface pressure is increased to shear the ball seat shear screws and pump the seat and the ball down into the well bottom. This method holds pressure from above only and can not hold pressure from below. For this reason another plug/barrier is needed to be run at the bottom of the tubing while dismantling the rig blow out preventor (BOP) and mounting the Christmas tree. Also some problems can happen when shearing the shear screws of the pump out plug due to completion fluid pressure differential across the ball, that leads to inaccurate shear value (either more or less than the predetermined pressure for shearing).
Accordingly, a need exists for a tool capable of performing various completion-related operations without requiring repeated pulling of the tool, or hiring of one or more specialists.